Thread: ?
View Single Post
Old 01-21-2016, 05:58 AM
  #3  
JohnBurke
Disinterested Third Party
 
Joined APC: Jun 2012
Posts: 5,926
Default

7. Airplanes with multiple engines can operate on less engines, and we do spend much of our time when training with an inoperative engine. Engine failures are quite rare, especially in turbine airline aircraft, but they do happen. Airline aircraft must be able to fly and climb with an engine inoperative, and we plan every takeoff with the idea that an engine could fail at the worst possible time. We plan for a failure at a low speed when we must stop on the runway, and we calculate the distance. We also plan for failures at higher speeds on takeoff, when we must continue the takeoff with that engine failed. An engine failure on takeoff is the worst possible time to lose an engine, so we focus on that in our planning.

A four engine airplane such as the Boeing 747 can lose an engine and continue flying, and it flies well on one engine. Loss of a second engine, especially on the same side of the airplane (both engines on the right wing, for example) is a big problem, though the airplane does remain controllable and can be landed. In training, we do cover making a two engine approach and landing, in the 747. That's as far as we go, however, and we don't train for three engines failed, or even four engines failed. It's happened...there have been extremely rare cases in which 747's lost all four engines due to volcanic ash, but again, it's very, very rare.

You may have heard the old joke about the man who hears the announcement from the captain that an engine has failed, but don't worry, we have three more, and we'll be an hour late. Some time later, a second announcement arrives that we've lost a second engine, but don't worry, the airplane flies fine on two engines, and we'll be two hours late. Some time later, another announcement comes; we've lost a third engine, we're okay, but we'll be three hours late.

The man turns to his traveling companion and says "great, if we lose the last one, we'll be up here all day."

One engine, not a problem. Two engines, it's a problem, but we can manage. We're diverting, landing, but we can do it. Three engines is a big problem. Four engines, we're going swimming or it's going to become a fairly short flight. Ironically, the 747 glides well for such a large airplane. There are fewer and fewer four engine airplanes, however, and the two-engine airplane is favored today.

We have multiple engines in aircraft partially for redundancy and safety, but primarily for performance. More thrust means greater performance. Today we have aircraft such as the 777 which don't use more engines, but bigger engines. If an engine is lost, there's only one left, but it's also a much bigger engine.

Losing engines isn't just a matter of losing thrust. Engines provide a lot of other things that are used in flight. We have hydraulic pumps that are used to operate flight controls, flaps, spoilers or speed brakes, landing gear, etc. We use compressed air from the engines ("bleed air") for pressurizing the airplane, heating cabin air, protecting the wings from ice in clouds, pressurizing oil and hydraulic tanks, etc. Engines have generators that supply large electrical loads that do everything from operate flight controls in some aircraft to light the cabin, power the radios, etc. On a large four engine airplane, losing an engine means losing a hydraulic system, a power source, bleed air, etc. That engine also uses oil to warm the fuel, which is important at high altitudes when fuel gets cold (and thick, and can develop ice in fuel filters and engine fuel controllers). Losing an engine affects many more things than just losing thrust.

8. That brings us to your statement on re-directing fuel. You're absolutely right. Fuel must be redirected in order to keep the amount of fuel in the wings balanced, and to ensure that the remaining engines have enough fuel. Multiple fuel tanks are used in large airplanes; they may be in the wings, in the fuselage, and sometimes even at the back of the fuselage. It's important to know where the fuel is and to manage it properly during the flight. Cross feeding, cross flowing, etc is important. With loss of an engine, fuel heating can also be important.

9. You're right; getting the landing gear lowered for landing is important, and it does provide drag which helps slow the airplane. The landing gear has airspeed limits; lowering it at too high a speed can damage some parts of the airplane, so it's important to stick to the limits. If an engine (or multiple engines) is inoperative, one may want to delay lowering the landing gear in some cases. There are other situations on short flights in heavy aircraft when one delays raising the landing gear, and lowers it early, to help cool the brakes.

10. 250 mph is usually too fast. The actual landing speed depends on weight and air temperature, runway conditions, and the elevation (or altitude) of the airport. Before beginning our descent from our cruise altitude, we do calculations to determine the proper speed for landing. We look at the weight we anticipate for landing, and along with the other factors just mentioned, calculate the speeds for extending flaps, and for actually landing. That speed also determines the amount of braking we'll need, along with the distance we need to get down and get stopped. Too fast and we will need more distance, and will have hotter brakes. Too fast and we may not get stopped. Brakes that get too hot may not work, either. There isn't one specific speed for landing, but it depends on the conditions of the flight.

If you can help in an emergency and you know what to do, you should help as much as you're able. Bear in mind that it's rare that there aren't several pilots riding on an airliner; in most all cases there are pilots riding in passenger seats, and often on a spare seat in the cockpit, as we go home or to work, and there are often private or commercially rated pilots on board, too. It would be very rare that both pilots in the cockpit are incapacitated, and there's nobody else on board who could fly the aircraft. Also bear in mind that if both pilots are incapacitated, it's unlikely the flight attendant would know...and the cockpit door is locked from inside.

Epilepsy doesn't take away from your ability to be a valuable and contributing member of society. It may affect what you can and can't do. We all have limitations. Most heros in the world go unrecognized, and they're found in every walk of life. Some of the most critical roles in the world aren't the most dramatic, but they're the most important. Deep down we'd all like to be something larger than life. I'd love to be a Navy SEAL. I've worked with them, have a great deal of admiration for them, but I won't ever be remotely anything like them, and that's okay. Some of the people I most look up to in the world are teachers. You don't need to perform a walter mitty fantasy of saving the day in an airliner to be important or valued, however, and you can and will contribute to the world by being you. I used to wish I could do something big, like most boys and young men. Something big turned out be having kids of my own, and leading a basic life; sometimes the biggest things are found in the most common elements of life. They don't make stories or movies about them, not always, but they're still some of the most critical building blocks of our daily lives. If you get the chance to save the day on an airliner and you're asked to do so, then step forward. But if you're never asked to do so, as 99.999999% of us will never be asked to do, then don't worry. You've got plenty in your life that will be just as heroic; the trick is learning to recognize it.
JohnBurke is offline